In-process inspection of semiconductor wafer surfaces is playing an ever increasing role in the fabrication of integrated circuits. With shrinking surface dimensions and the increasing number of components per chip, various inspection techniques are now used to monitor for defects and contaminants on the surface of semiconductor wafers during production in an effort to increase yields. Since the features on the wafers are on the order of microns, even very small particulates (e.g., dust, silicon chips, photoresist flakes, etc.) can ruin an otherwise acceptable device. Determination of the presence and location of any contaminants on the wafer surface can (1) aid in locating the source of the contamination in order to prevent future contamination, and (2) assist in determining whether or not to discard a particular wafer due to excessive contamination that can lead to the failure of many or most of the devices on the wafer.
Small particles are difficult to see when various circuit patterns are present on the wafer. An operator must scrutinize the inspected area in detail to determine defects from the patterned background of the wafer surface. Such a technique is tedious and time consuming resulting in operator fatigue and errors. Additionally, inspections are presently carried out manually by operators viewing the wafers using standard reflection mode optical microscopes. Although such manual techniques work well, they are time consuming and only a small number of circuit areas on a limited number of wafers can be inspected. For statistical purposes such sampling is too small.
Accordingly, there is a need for a wafer inspection technique that can readily discriminate between the contaminating particulate and the features or patterns on the wafer surface. Additionally, such a technique should be able to detect the particulates contaminating the surface of a wafer while automatically recording, the real-time, the position and size of the particulate.